Great Britain, the country that, during the Industrial Revolution, got the rest of the world hooked on burning coal, is planning to end its own dependence on the dirtiest of fossil fuels. Drax, the operator of Britain’s largest coal-fired power plant, plans to stop using coal by 2020, in line with the country’s effort to phase out coal entirely by 2025.

How will Britain make this happen? In part, by switching to biomass, largely in the form of wood pellets. Biomass already accounts for about 8 percent of UK electricity generation, four times as much as coal does. This step away from coal is a good one, but biomass carries costs of its own -- for the climate and the environment -- and those costs need to be recognized and accounted for.

Like the rest of Europe, the UK considers biomass to be a zero-carbon fuel. But the calculation involved includes a big loophole in the way the European Union accounts for carbon dioxide emissions: Member states are allowed to count only those emissions produced during wood pellet production and transportation, and to ignore those that come from burning the pellets to make energy.

The EU is well aware that those emissions occur, but assumes that the trees that sprout up to replace the ones used to make pellets will, over the course of a few decades, absorb as much atmospheric carbon as is produced by pellet burning. And the market demand for wood pellets will work to ensure that new trees are continually planted.

This makes some sense in theory: A growing market for wood does make it profitable for landowners to keep planting more trees. This should be especially true when the harvested wood is used for pellets, because they’re supposed to be made largely from waste wood -- those parts of trees that are unsuitable for lumber or other purposes and otherwise would be discarded.

Biomass proponents point to a 2015 study showing that, when the larger life cycle of trees is taken into account, burning wood instead of coal could reduce greenhouse-gas emissions by 74 to 85 percent.

The problem is, this elides the risk posed by near-term emissions spikes. When an older tree is cut down and burned, it releases a lot of carbon dioxide all at once. It takes much longer for a new tree to absorb the same amount.

The EU’s calculation also fails to account for the carbon lost from soil when trees are cut down. Interestingly, this is a cost that is imposed most heavily on the US, where 60 percent of the wood used in Europe is grown. (Wood pellet exports nearly doubled from 2012 to 2014.) There’s also a wider risk to US forests -- though pellet makers claim to use only low-grade wood, investigations by the Natural Resources Defense Council, the Southern Environment Law Center and the Wall Street Journal have independently shown that hardwood is regularly harvested from the Southeast’s most ecologically sensitive forests.

Once transported to Europe, the pellets impose additional unrecognized costs. Biomass produces less carbon dioxide than coal when it’s burned, but it is also less energy-dense, so more of it needs to be burned to create the same amount of energy. Burning pellets emit both carbon dioxide and particulate pollution (though fewer toxic heavy metals than coal), which gets into the lungs of people living near biomass power plants.

Of course, it would not pay for the UK or the EU to return to coal. But they should account realistically for the environmental costs of alternative fuels. The EU needs stronger mechanisms to keep track of wood pellet sources -- the type of trees and forests they come from, and to what extent the harvested trees are replaced with new plantings. And EU ledgers need to fully account for the emissions created by burning biomass. The move away from coal is welcome, but it should also be toward more transparent and responsible power generation.

By Tatiana Schlossberg

Tatiana Schlossberg, a former New York Times science reporter, writes about climate change and the environment. -- Ed.